Santa Clara Valley Water District Sierra Negrete {CSU, Chico} Dave D. Drury, P.E. {SCVWD} Carrie Monohan, Ph.D. {CSU, Chico; Sierra Fund} Stephen A. McCord, Ph.D., P.E. {McCord Environmental}

Elemental The Site Mercury Hg(0) Calero reservoir, located in San Jose, California, on Calero Creek, is listed as an impaired water body. The extensive mining done along the Coastal Ranges of California has exposed mercury to the surrounding watersheds, including the Guadalupe River Watershed where Calero Reservoir is located. The reservoir is Inorganic Methyl Mercury 2.2 miles long with a capacity to hold 9,934 acre-feet of water. Mercury (HgII) (CH3Hg)

The Construcon of the Calero Dam in September 1935 (SCVWD,2015)

Parcle Bound Purpose of Study Mercury (HgP) To compare the concentraons of dissolved oxygen with the concentraons of methyl mercury in the hypolimnec zone of the Calero reservoir in an effort to gauge the impact of the Hypolimnec Oxygenaon System used to treat mercury-impacted waters. Methyl Mercury Producon Methods Data •Oxidaon-reducon reacons -Elemental mercury Hg(0) is Profiling oxidized into inorganic mercury (HgII) where it can aach to a Water column profile done using the Hydro-Lab DS5 sonde at intervals of a Calero Reservoir May 2013-’14 Calero Reservoir June 2013’-14 methyl group or evaporate into the atmosphere and can be quarter of a meter to one-meter depth specific to each strafied layer of the reduced back to elemental mercury. reservoir. • Epilimnion: measurements were taken at every meter. •Methylaon-demethylaon processes -Through the • Thermocline: measurements were taken at ¼-meter intervals Reference map of the Calero Reservoir in San Jose, CA methylaon process, inorganic mercury (HgII) transforms into • Hypolimnion: at one-meter intervals methyl mercury through bacteria. The reverse of this process

Hypolimnec Oxygenaon System is known as demethylaon. The HOS system is designed to diffuse oxygen into reservoir’s hypolimnion in an Water quality parameters measured during profiling with the sonde were effort to increase the dissolved oxygen level and inhibit the formaon of methyl recorded digitally and on site: (Ministry for the Environment, 2008 and USEPA, 2014) mercury. For this study, the HOS system operated from May to October of 2014. • Temperature* • pH * Parameters of • Oxidaon-Reducon Potenal interest for this Calero Reservoir July 2013-’14 Calero Reservoir August 2013-’14 • Specific Conducvity study • Dissolved Oxygen* Discussion • Chlorophyll • Fine oxygen bubbles emanang from the diffuser line rose slowly through the water column, diffusing oxygen into the water while Sampling entraining ambient water into its plume. Water samples were collected 1-3 mes a month for total and methyl mercury • The vercal profile of dissolved oxygen determines methyl throughout the year 2014 (Drury, 2013). mercury producon in the water column and the diffusion • Epilimnion interacon with the sediment bed. • Mid-Epilimnion** • As dissolved oxygen decreases, methyl mercury begins to form. This response is not immediate but instead the data indicates • Metalimnion ** Collected May-Nov Vercal profiles of dissolved oxygen and methyl mercury concentraons for there is a me lag between dissolved oxygen fluctuaon in • Mid-Hypolimnion** the months of May-August during a 2013 and 2014. The Hypolimnec • Hypolimnion Oxygenaon System was operang full me during the year 2014. concentraons and the producon of methyl mercury. The Calero Oxygen Diffusion Line Length and Elevaon (Drury, 2013) The Diffuser Line Diagram (Mobley Engineering, 2014). Water sample analysis Oxygen Diffusion Line • Total methyl mercury concentraon- EPA Method 1630 Conclusion (praccal quanficaon limit of 0.050ng/L) A long-term study of the Hypolimnec Oxygenaon System at The diffusion line is anchored with concrete blocks one foot from the boom of the Calero reservoir is needed to further invesgate the the reservoir. During the me of operaon, the system diffuses oxygen at a rate effecveness of oxygen diffusion into anoxic regions of lakes of 12.5 scfm through a line extending the length of 1000 (Drury, 2013). Results and reservoirs and its ability to reduce methyl mercury. Temperature • Monthly temperature profiles show that the surface waters in the Calero reservoir ranged from 9°C to 25°C through the year of 2014. • The metalimnion zone of the water column ranged from 5 to 10 References meters. Within the metalimnion a thermocline developed with A comparison between dissolved oxygen and methyl mercury 1. California Regional Water Quality Control Board San Francisco Bay Region (SFCRWQCB). Guadalupe River Watershed Mercury Total temperature fluctuaons increasing from the months of February concentraons in the Calero reservoir during 2013, the year before full- me operaon of the Hypolimnec Oxygenaon System . Maximum Daily Load (TMDL) Project: Basin Plan Amendment. to September. 2008. • The hypolimnion maintained a temperature range of 9°C to 19°C through the year. 2. Chrystall, Leila. et Al. Ministry for the Environment. Mercury Inventory for New Zealand: 2008. Mercury in the New Zealand Dissolved Oxygen Environment:2 Mercury in the Environment. 2009. • Dissolved oxygen concentraons were maintained equal to or 3. Drury, Dave. Methyl Mercury Producon and Control in Lake and greater than 1.0 mg/L at or above the elevaon of the oxygen Reservoirs Contaminated By Historic Mining Acvies in the Historical Concentraons of Methyl Mercury in the Calero diffuser during the months of May-October, 2014 when the system Guadalupe River Watershed. 2013. Reservoir and the Target TMDL of 1.5ng/L (Drury, 2013). was in operaon. 4. Mobley Engineering. Line Diffuser Operang and Maintenance Mercury Reducon Goal Methyl Mercury Manual with System Operaon Recommendaons. 2014. Under the Guadalupe River Watershed Mercury TMDL, Calero Reservoir’s • Methyl mercury concentraons in the hypolimnion ranged from seasonal maximum concentraon shall be less than 1.5ng of total methyl A comparison between dissolved oxygen and methyl mercury concentraons 5. United States Environmental Protecon Agency. Mercury Study undetected concentraons to 0.5 ng/L throughout the year of 2014 in the Calero reservior during 2014, the year of full-me operaon of the Report to Congress. Volume III: Fate and Transport of Mercury in mercury per liter of water in the hypolimnion (SFCRWQCB, 2008). and remained below the TMDL target concentraon of 1.5 ng/L. Hypolimnec Oxygenaon System. the Environment. 1997.